The long-term objective of this project is to study how single binocular vision is achieved by the fusional mechanism in humans. The nature of sensory compensation during fusional response is of particular interest. To that end, a systematic study of the following is proposed: 1. Sensory interaction in the spatial frequency and disparity domains. 2. The spatial extent and orientational characteristics of sensory interaction. 3. The role of fusional stress in the modification of perceived visual direction associated with a particular retinal regions during forced vergence. The understanding of sensory interaction during fusional compensation is fundamentally important to the characterization of the nature of disparity processing within Panum's fusional areas.